A conventional hybrid construction machine is known to regenerate energy by utilizing hydraulic oil introduced from a turning motor and rotating a hydraulic motor.
It is disclosed in JP2009-281525A that an electromagnetic switching valve is switched to an open position for turning regeneration and an opening of a proportional electromagnetic throttle valve provided in parallel to a safety valve is controlled to reduce passage resistance caused by the safety valve when a pressure signal of a pressure sensor for detecting a turning pressure at the time of rotating a turning motor or a braking pressure at the time of braking reaches a pressure set in advance.